Clearing of rocks in agricultural fields has been an activity going back to antiquity. Early methods involved picks, shovels, horse drawn ‘stone boats’ and always a good deal of manual labour. More modern farming waged war on rocks with such devices as the rock rake, the rock windrower and the rock picker, all used to lessen the manual labour and time components of rock removal. Interestingly, and almost in surrender, perhaps the most practiced approach to the problem of field rocks, is not to remove them at all! This is accomplished, or not accomplished, using a long heavy steel water filled roller, much like a giant rolling pin, but pulled behind a tractor and, when the field is damp, knocking the rocks just below the surface of the soil, out of sight, at least for a time. Of course, invariably, the rocks do return to pose a hazard to agricultural equipment through field tillage, or by natural processes such as frost heaving. Eventually, through repeated rolling, some fields may begin to resemble hard-packed cobblestone parking lots as more and more rocks are thrust up from deeper in the soil.
For rock removal, various devices are available, mainly the rock windrower used in combination with the rock picker. The rock windrower consists of a horizontal rotating drum set at an angle of perhaps 30 to 40 degrees to the direction of travel as it is towed behind a tractor. The rotating drum has a series of hardened steel teeth that bunt loose rocks forward and to the side eventually kicking them out along side of the machine to form a row of rocks. This is a vigorous and slow moving process though with the teeth battering the rocks innumerable times as they progress down the rotating drum and are finally launched out the side of the windrower. Depending on the soil type, the rocks may roll for some distance and may form scattered wide rows that may later be difficult to pick up by the partnering machine, the rock picker. The rock windrower may be used in a tilled or summer fallowed field free of large amounts of stems or plant debris. It is however not usable in hayfields or other fields that may contain any significant amount of field debris as these tend to wrap around the rotating drum clogging the teeth and rendering the machine ineffective.
There is also the landscape rake—much like a heavy duty garden rake—that is used more effectively on roots and branches than on rocks. As well, there is the rotary or stick rake. There are really two types of these, one that is fairly light duty and similar to a rotary hay rake intended to be used mainly for windrowing fallen branches, and a much heavier duty version that is mainly intended to unearth and windrow tree roots but is also somewhat effective on rocks. This machine is massive though, more resembling earth moving or mining equipment than agricultural and no doubt costly. These machines are also very aggressive and till up the soil and therefore are not useful for removing rocks in hayfields without damaging the perennial forage of the hayfield. Like the rock windrower, these machines must also be operated at slow speeds perhaps in the realm of 3 to 4 mph.
There are also various designs of front-end-loader buckets that have grates or tines for skimming the surface and screening out debris and smaller rocks and then used for dumping the remaining rocks into an awaiting dump truck. These are of course limited to the width of the front-end-loader of the tractor and are mainly used for smaller areas and roadways and certainly not for acres of farm fields.
The rock picker is the machine to use for picking up rows of rocks. Having a pick-up width of typically only about 4 to 5 feet, it is effectively used with some form of rock windrowing machine, and not on its own for clearing rocks in a field. Powered and towed by a tractor, the rock picker picks up rocks that have been rowed, screens out smaller rocks, soil and smaller debris collecting the remaining rocks in a bin or hopper that is part of the rock picker machine. Once the bin is full of rocks, the rock picker may be towed off the field where the bin is tilted and the rocks are dumped out of the back end of the machine. The rock picker is considered to be a cooperating and not a competing device to the rock windrower including the device of the present invention, in the process of clearing rocks from fields.